Enzymatic conversion of cellulosic fibers



June 1962 w. BOLASKI ET AL 3,041,246

ENZYMATIC CONVERSION OF CELLULOSIC FIBERS Filed Dec. 28, 1959 3Sheets-Sheet 1 MAG 550 X MAC 550 X 1% I E l INVENTORS WALTER BOLASKI BYJAMES C.GALLATIN IR.

ATTORNEY June 26, 1962 w. BOLASKI ET AL 3,041,246

ENZYMATIC CONVERSION OF CELLULOSIC FIBERS Filed Dec. 28, 1959 I5Sheets-Sheet 2 MAG '550 X :E Q Lb WALTEQ 5555 :mmes c. ALLATIN R.

ATTORNEY W. BOLASKI ETAL ENZYMATIC CONVERSION OF CELLULOSIC FIBERS June26, 1962 5 Sheets-Sheet 3 Filed Dec. 28, 1959 MAG. lpoox m S RI w m NMAmLu N e 5 mm AA W3 Y B United ttes setts Filed Dec. 28, 1959, Ser. No.862,427 4 Claims. (Cl. 195--8) The present invention relates to new anduseful improvements in papermaking and is directed more particularly toa novel process for conditioning and enhancing the papermakingcharacteristics of cellulosic papermaking fibers, such as cotton lintersor the like, by improving their fibrillation.

For purposes of definition, fibrillation, as employed herein, will beunderstood to mean the separating and rearranging of fibrils and/ orsegments of fibrils of a parent fiber.

It is generally appreciated that the strength of ordinary paper residesprimarily in the bonds between the fibers. The intimate bringingtogether of fiber elements is necessary for the formation of strongbonds in paper. An increase in fibrillation, resulting from an increasein the conventional beating action, has promoted more exten sive bondingbetween the fibers. As the degree of beating is extended, the strengthof the paper attains a maximum value, beyond which increments in thedegree of beating cause proportionate decreases in strength.

By the invention hereof, the fibers are so conditioned, throughincreased surface fibrillation, as to lead to an immeasurably improveddegree of fiber contact resulting in a vastly greater number ofpotential bonding points in the process of making a paper web.

For optimum strength development a desideratum in fibrillation is tobreak down the fibers into fiber-like segments or fibrils of smallerdiameter in such manner as not to create new surfaces to any appreciableextent and rather to expose already-existent surfaces in the celluloseupon the saturation thereof in a fluid.

The invention relates particularly to a novel enzymatic conversion ofcellulosic papermaking fibers, such as unpurified or purified cottonlinters, wherein the fibrils are separated or rearranged so that theirfunctional characteristics are improved for subsequent conditioning andworking.

More specifically, the invention comprises a method of or process fordeveloping strength in such fibers by altering their condition throughtheir conversion by enzymatic activity in order to obtain fibrillationWithout appreciable shortening of fibers in an economical andexpeditious manner and the product of such method or process whichpossesses the desired strength characteristics and properties, all asexemplified in the detailed disclosure hereinafter set forth,

Stated otherwise, the invention contemplates a method of causing aconcentration of enzymes, preferentially in the form of an aqueousdispersion or solution thereof, and prepared from one of thecarbohydrolytic type enzymes, such as cellulase, to act on cellulosicfibers so as to produce fibrillation. It will be understood that theinvention is adapted for use in fibrillating various celluatent losicfibers, such as raw or purified cotton lint fibers, bast fibers, such ashemp, flax, manila, and the like, regenerated cellulose fibers, fibersderived from whole stems such as straw, esparto, bamboo and the like,and fibers derived from wood.

Commercial methods of fibrillation have been heretofore developed but inmost cases such methods have been exceedingly slow and laborious and thenature of the treatment has been often such as to impair the quality ofthe fiber and to produce a low yield, loss of fiber strength, decreasein length of fiber, and the like.

This invention envisions the manufacture of enzymetreated cellulosicfibers and fibrous materials prepared therefrom, and is directedparticularly to a method for improving the strength of felted fibrouscellulosic materials, such as paper and the like, by fiber alterationand fibrillation.

A salient object hereof is the provision of a method to control thedegree of fiber alteration and fibrillation by controlling the enzymicaction to a desired level, all depending upon the desideratum in the endproduct.

Another object of the invention is to provide a method offering anability to produce paper by by-passing, or at least minimizing, theconventional processing and refining techniques in stock preparation.

A major role of fibrillation in producing strength is to provide greatersurface tension forces having a capacity for drawing fiber surfaces intosufiiciently close proximity for bonds to be established. With theincreased fibrillation afforded by the invention hereof, the fiberflexibility and conformability of the surfaces is increased and hencesurface tension forces during drying will produce more bondable areas.

The process of alteration envisioned herein is one which ensues under orin the presence of a liquid, a requisite for fiber swelling which is soall important in the ultimate development of strength in paper.

We employ a substantial excess of water with respect to the amount offiber under treatment, the exact amount of water used being subject toconsiderable variation. In preferred practice, we employ a consistencyof approximately 6% of fiber material.

Through the use of such a fluid, the swelling of the cellulose combinedwith the dimensional swelling of the fiber results in an opening up ofthe fiber structure.

The fluid penetrates the interfiber capillaries, and as the fiberswelling increases, the fiber structure is transformed into a morehighly plasticized state wherefor fiber flexibility becomes greater andimproved conformability of the fiber is made possible.

As conceived, this alteration or conversion is carried out to a degreewhere subsequent dispersion and minimum mechanical disintegration willexpose the minute fibrils of the fibers and enhance their papermakingcharacteristics by increasing the potential for interfiber contactthrough the concomitant increase in the number of potential bondingpoints. The resulting fibrillar arrangement and/or rearrangement is suchas to develop strength in cotton linter papers comparable to thatexhibited by cotton lint fibers and/ or cotton cutting papers.

Rag content paper manufacturers have recognized that the supply of goodrag cuttings is dwindling, a condition brought about largely through theuse of synthetic fibers as substitutes for, or replacements for, cottonfibers.

3 Looking toward the future, the time is foreseen when sulficient ragsto meet the needs of the papermaker will not be available.

A new source of cellulosic fibers, suitable to papermakers requirements,has been obviously essential for some time. The most promising sourceappears to be cotton linters because of their morphological similarityto cotton lint fiber. At the present time, cotton linters constitutemore than 20% of the total cotton fiber used by rag paper mills. Thisfiber can be cooked and bleached so that it is satisfactory from thestandpoint of the purity of the cellulose. Because the fiber isinherently stiffer, more wiry, and appreciably shorter than lint fibers,it does not provide strength comparable to that provided by good cottonrags.

Many efforts have been directed to improve the papermakingcharacteristics of cotton linters. Heretofore, the solution to theproblem of obtaining improved strength in cotton linters has seemed tolie in chemical modification, ultrasonic disintegration, modification ofpresent processes, modification in present equipment, or use ofequipment of an entirely different type. These present methods are alikein that each process is variable and difiicult to control and each isrelatively slow in effecting fibrillation and developing strength in thecotton linter fiber.

From the economic standpoint, the cost of these processes or methodsincreases the cost of cotton linters, although per-formancewise, theyappear to most persons skilled in the art to be somewhat superior tounmodified cotton linters.

Advantages hereof other than those described above will I be apparentfrom the following description and claims taken together with theaccompanying drawings wherein: FIG. 1 is a diagrammatic plan viewshowing typical papermaking cotton linter fibers without any exposure toenzymatic action;

FIG. 2 is a diagrammatic plan view showing enzyme treated cotton linterfibers with a low order of fibrillation following a minimum of enzymaticaction according to our invention;

FIGS. 3 and 4 are diagrammatic plan views showing enzyme treated cottonlinter fibers with degrees of fibrillation greater than illustrated inFIG. 2 according to our invention; and

FIG. 5 is a diagrammatic plan view showing the extensive fibrillation ofan enzyme treated cotton linter fiber according to our invention.

While, as above noted, our improved process involving enzyme-exposure isapplicable to the fibrillation of fibers, and in particular cottonlinters, it will be referred to specifically below as involving thefollowing steps:

A preliminary treatment of the cotton linters will appreciably reducethe time and ease of subsequent treatment and may comprise a wettingoperation for purposes of plasticizing the fibers and causing theamorphous areas thereof to swell.

The wetting has the capacity of extending the areas adjacent thecellulose molecules and to enlarge the broken ends, deep cracks, andabraded areas. This extension permits the enzyme to penetrate the fiberdirectly through the fiber Wall and to separate and break the cellulosicchains to individual fibrils or groups of fibrils that adhere to theparent fiber.

An excess of solution is desirable, particularly where the operation iscarried out on a large scale. This permits the maintenance of a moreuniform concentration of treating solution at all points throughout thereacting vessel, and insures a uniform treatment of the fibrous materialthroughout the batch.

The concentration of enzymes of the carbohydrolytic type may beintroduced to the liquid in the reacting vessel before or after theaddition of the fibers.

Typical of the enzymes defined as of this genus is the cellulase enzyme.

The cellulase enzyme may be produced from a culture of Aspergillus nigerand may be crystallized in one or several steps or stages ofpurification.

Insofar as purification is concerned, suffice to say that the morepurified the enzyme, the less that is required for use. Contrariwise,the lesser the degree of purification, the greater the quantity requiredfor use.

Enzymes are powerful catalysts with high reaction rates. Their reactionrate is instantaneous as of the moment they are contacted with thefibers assuming that all factors, hereinafter discussed, are at theirproper levels.

The following gives one specific example to illustrate one method ofproducing the fibrillation of this invention, it being understood thatother adjuvant materials may be similarly incorporated and that thequantities and types of substances added to the materials mentionedherein may be varied.

In the practice of our invention, water is heated to a temperature of98.6 F. and is thoroughly mixed with a suitable acid, acid salt or saltcapable of acid hydrolysis added in such quantity as to bring the waterto the optimum hydrogen ion concentration corresponding to a pH of 4.0.At this point, it is desirable to stir the solution and introducethereto 0.01%-2.0% of cellulase enzyme based on fiber Weight and to addsufficient cotton linter fibers to obtain a consistency of from 3.0 to8.0%. This mixture is maintained at the temperature noted above andmildly agitated Within the reacting vessel throughout the enzymicconversion cycle.

A sufficient quantity of enzymes is preferentially employed to permitthe solution intimately to contact all portions of the fiber materialbeing treated and thereby insure the desired uniformity of penetration.In this connection, it has been found requisite to employ some agitationsystem by means of which the solution is carried into intimate contactwith the fiber materials.

Without such stirring, which may be the equivalent of normal beateragitation, a localized action could result.

When the procedure thus outlined is followed, fibrillation of cottonlinter fibers is noted in about /2 hour and continues to any desireddegree until inactivated by one of various means, such as hightemperature or the addition of chlorine.

It is known that factors affecting the activity of the enzymes includes:(1) time, (2) concentration, (3) temperature, (4) hydrogen ionconcentration, and (5) activity of the particular enzyme employed.

indicated that the reaction has exceeded optimum limits,

sclame excessive disintegration of the fibers having taken p ace.

It will be appreciated, however, that for types of paper, other than theaforesaid fine writing papers, different reaction times may be moredesirable.

Sufiice to say that in the case of the above illustration, cottonlinters so treated produced a pronounced degree of fibrillation ascompared with untreated cotton linters agitated in the conventionalmanner during a like time period.

Concentration The rate of attack upon the cotton linters is dependentupon the concentration of the enzyme employed. Generally speaking, wheretime is an important factor, the

reaction rate may be increased by using enzymes in greater proportion.It is obviously primarily an economic consideration as to what theoptimum operating conditions as to concentration are.

We have determined that a range of 01% to 2% (weight of enzyme to weightof fiber) may be employed.

By way of illustration, at the lower extreme of this range, .135 poundof enzymes may be added to 1350 pounds of cotton linters. At the higherextreme of this range, 27 pounds of enzymes may be added to 1350 poundsof cotton linters.

To go lower or higher and without the specified range would beeconomically impractical insofar as results are concerned.

Temperature Enzymes are considered to be complex proteinaceous organicmolecules and as such are sensitive to temperature.

The fibers are treated, according to the present invention, attemperatures in the range of 90 to 100 F. The reaction proceeds mostrapidly in such range and preferably in the area of body heat, i. c.98.6".

At temperatures below 90 F, the reaction time required is sharplyextended and, accordingly, it is preferable not to operate thereat,fibrillation not proceeding at an appreciable rate. Higher temperaturesdo not provide economical gains. Beyond 100 F., their activity decreasesrapidly, and beyond 110 F., fibrillation does not proceed at anappreciable rate.

The particular temperature in the range of 90 to 100 F. is selectedaccording to the particular material treated, the concentration ofenzyme used, and the time of treatment.

At temperatures above 98.6 F., the time period of treatment is shortenedat some sacrifice to fiber quality but the quality remains good up to100 F.

Hydrogen Ion Concentration Every enzyme has a pH range at which it ismost effective and it usually loses most of this activity at a slightlydifferent pH.

The enzymes hereof show their maximum activity at an acidic pH withoptimum activity at a pH of 4.0. The resulting efficiency, whenoperating above pH 7.0, is such as to impair the activity of theenzymes.

Buffering agents, such as potassium acid phthalate or other salts and/orcombinations thereof, may be added to the preparation in appropriatequantities to reduce the pH to the desired level and to maintain itthereat.

With specific reference now to the attached drawings, in FIG. 1, thereis shown a groupment of typical cotton linter fibers, untreatedaccording to the invention hereof. That is, this is a showing of fibersbefore alteration. The frayed end of a fiber is illustrated at 10. Thecracks within the fiber are illustrated at 12. The abraded area,delineated by reference numeral 14, shows an appreciable degree of fiberinjury.

In FIG. 2, we have illustrated typical cotton linter fibers treated withthe cellulase enzyme and showing the fiber swelling and surfacefibrillation when compared with the fibers shown in FIG. 1.

The increase of exposed fiber surface area can be noted at 20, samehaving been caused by the longitudinal separation or splitting off ofthe slender fibrils from the main body of the fiber. Initial liberationof fibrils is plainly visible, it being readily obvious that thetendency of the fibers is to split lengthwise into fibrils. Fibrilagglomerates can be observed at 22.

In FIGS. 3 and 4, a pronounced increase of fiber swelling and anincrease of exposed fiber surface area is observable. The brooming orfraying of fiber ends is shown at 40 in FIG. 4. The increase of attachedlongitudinal fibrils of the fibers is shown at 42, the very completelongitudinal splitting of the fibers being plainly seen.

Surface degradation as shown by the burred edge of the fiber isindicated at 34 in FIG. 3 and at 44 in FIG. 4.

The external surfaces of the fibrils provide the locations for potentialinterfiber bonding in the entanglement process of forming a paper web.

A sufiiciency of fibrils for bonding back to the surfaces of the parentfiber, or of adjacent fibrils or to the surfaces of other parent fibersor fibrils thereof, is readily observable.

In FIG. 5, the arrangement of the fibrils within the cellulose fiber isillustrated at 50. The longitudinal separation or splitting of theslender fibrils is shown atSZ.

Normally the fibrils are attached to the parent fiber. On occasion, someof the fibrils may be completely detached.

In FIG. 5 is clearly illustrated the ribbon-like arrangement of thefibrils or building units, as they are sometimes called, in the nativecellulose fiber.

Since certain changes may be made in the above process and product andthe specific example of the practice of the invention Without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description shall be interpreted as beingmerely illustrative and not as being limiting.

It is not intended thereby to have this invention limited to orcircumscribed by the specific details of materials, proportions, orconditions herein specified, it being agreed that this invention may bemodified according to individual preference or conditions withoutnecessarily departing from the spirit of this disclosure and the scopeof the subjoined claims.

Having thus described our invention and the best manner of practicingthe new process for forming the novel composition thereof, all withoutlimiting ourselves to the order of steps of such process recited, or tothe proportions of parts employed therein, or to the precise in- Igredients named therein, as it is evident that each of these ingredientsnamed therein has a considerable range of equivalents and as it isfurther evident that the order of steps and proportions of partsemployed may be varied without departing from the scope and purposehereof, what it is desired to claim and secure by Letters Patent of theUnited States is:

1. In the process of preparing a finished paper sheet, the improvementcomprising, the altering of the papermaking fibers through thefibrillation thereof by a proc ess which comprises treating the fibersin a bath of cellulase enzymes ranging in amount between 0.0 1% and 2.0%by weight to the weight of the cellulosic fibers treated and maintainedat a temperature between F. and F. in a hydrogen ion concentrationcorresponding to a pH substantially at 4.0 during an enzymic conversioncycle not exceeding 5 hours.

2. In a method of preparing a paper sheet characterized by an increasein Mullen value, tear and fold, the improvement comprising, preparingsheet paper formed from an aqueous slurry formed with papermaking fibersaltered through the fibrillation thereof by a process which comprisestreating the fibers in a bath of cellulase enzymes, ranging between0.01% and 2.0% by weight to the weight of the cellulosic fibers treated,the bath being maintained at a temperature between 90 F. and 100 F. andat a hydrogen ion concentration corresponding to a pH substantially at4.0 during an enzymic conversion cycle not exceeding 5 hours.

3. In a process of making a finished paper sheet, an improvement in abiochemical process for conditioning the papermaking fibers comprising,the altering of the papermaking fibers through the fibrillation thereofby a process which comprises treating the fibers in an aqueousfibrillating bath of cellulase enzymes ranging in amount between 0.01%and 2.0% by weight to the Weight of the cellulosic fibers treated andbeing maintained in the bath at a temperature between 90 F. and 100 F.and in a hydrogen ion concentration corresponding to a pH subof thecellulosic fibers to filaments and having a consistency of from 3.0 to8.0% and comprising 0.01% to 2.0% enzyme based on fiber weight andagitating same at a temperature of within the range of 90 F. and 100 F.and at a pH substantially of 4 during an enzymic conversion cycle notexceeding 5 hours.

References Cited in the file of this patent Reese et al.: TextileResearch Journal, volume XXVII, No. 8, August 1957, pp. 626 to 632.

Marsh: Textile Research Journal, volume XXVII, N0. 11, November 1957,pp. 913 to 916.

Blum et al.: Textile Research Journal, volume 10 XXII, No. 3, March1952, pp. 178 to 191.

1. IN THE PROCESS OF PREPARING A FINISHED PAPER SHEET, THE IMPROVEMENTCOMPRISING, THE ALTERING OF THE PAPERMAKING FIBERS THROUGH THEFIBRILLATION THEREOF BY A PROCCESS WHICH COMPRISES TREATING THE FIBERSIN A BATH OF CELLULASE ENZYMES RANGING IN AMOUNT BETWEEN 0.01% AND 2.0%BY WEIGHT TO THE WEIGHT OF THE CELLULOSIC FIBERS TREATED AND MAINTAINEDAT A TEMPERATURE BETWEEN 90*F. AND 100*F. IN A HYDROGEN IONCONCENTRATION CORRESPONDING TO A PH SUBSTANTIALLY AT 4.0 DURING ANENZYMIC CONVERSION CYCLE NOT EXCEEDING 5 HOURS.